The rapid expansion of Amazon.com's U.S. warehouse network has brought eager tax concessions from job-hungry communities that hope to land plenty of fulltime $10-12/hour jobs (and many more in the seasonal Christmas rush) for unskilled and low-skilled workers, replacing entry-level and laboring jobs that used to be available at ailing retail stores and vanished factories.

How many jobs? The trend seems to be fewer, as Amazon builds more:

Up til recently, Amazon routinely advertised 1,000 or more fuilltime jobs at its million-square-foot facilities in Pennsylvania, Indiana and other early-adopter states.

Amazon is projecting just 750 jobs at its million-sq-ft facility in Robbinsville, NJ, near Trenton.

Why the drop? The company doesn't much talk about its local plans, leaving that up to local officials and outside Amazon-watchers. We do know Amazon has been buying warehouse robot systems and cutting costs by investing in machines, like manufacturers.

Update: "Ecommerce is labor-intensive – there are many steps in sorting, shelving, picking, packing, shipping," Fiona Dias, chief strategy officer at Amazon rival Kynetic's ShopRunner service in West Conshohocken.

But even Amazon's Kiva warehouse robots "are very expensive and have limits in their application," she added. Robots work best "picking many identically sized items," as at a factory, "not lots of different size packages" as in a retail fulfillment center.